1. Field of the Invention
The present invention relates generally to the robotic mapping of voids, and more particularly, the present invention relates to robotic devices capable of navigating and mapping voids in two or three dimensions and methods for deploying the robots, generating and capturing mapping data, and post processing the map data into usable formats.
2. Description of the Background
In many different fields of endeavor, it is highly desirable to discern the internal features of hollow, or partially hollow structures. These hollow structures, referred to herein as “voids” take on a variety of different common forms. Examples of voids include stand-alone discrete structures such as tanks and bunkers, man-made subterranean structures such as pipes (e.g., sewer pipes) and tunnels, and natural or dug structures such as caves and mines.
Often, the internal features of these structures are not accessible for observation by humans or by conventional technologies. For example, a bunker or storage facility may include residual or active radiological (e.g., nuclear) material that could harm a human surveyor. Further, some voids, such as mines or caves may be unsafe for human exploration because of past or imminent collapses. Additionally, some voids, such as sewer pipes may be too small for conventional surveying methodologies.
In the past, the mapping of the internal features of these and other voids has been attempted from the outside, via some type of penetrating technology, such as radar mapping. Many different technologies have been tried, to varying degrees of success, but none approach the resolution desired to produce useful internal maps.
The maps of the internal structures of various voids are useful for a variety of different reasons. Its use for mines is well documented and will be used as an example throughout this specification.
The mining of ores from the earth is an ancient process, having been practiced from prehistoric times. With the passage of time, mining became more widespread and technology evolved to allow mines to become ever longer and to go more deeply into the ground. It is now commonplace for a single mine to have many miles of excavated corridors.
When an ore of value is discovered in one place, there is often a high probability that either the seam of ore will continue from beneath one parcel of real estate to another, or that another seam of the same ore will be located under a plot of land that is near to where the original seam was discovered. It is therefore very common for numerous mines to be located in relatively close proximity to one another.
Once the valuable ores have been removed from a mine, it is almost never economically feasible or technically viable to refill the excavated void. As a result, mines that are below water table frequently fill up with water over the course of years, or toxic gasses can seep from the surrounding geology into the void. Quite frequently, the old mine shafts are used for the disposal of materials that are no longer wanted. Abandoned mines therefore are quite hazardous and governmental regulation attempts to minimize the likelihood that the construction of a new mine will intersect an existing mine and allow the potentially hazardous contents of the older mine to intrude into the newer one. The result of inadvertent breach from one mine into another is likely to be disastrous, with frequent loss of not only significant investment but also of human life.
In order to ensure that new mines do not penetrate into existing mines, the government generally requires that the excavator of the new mine obtain a permit before any excavation can begin. Part of the process of obtaining a permit for digging a new mine includes demonstrating that the proposed new mine will not intersect an existing mine. This is accomplished primarily by inspecting copies of existing maps of all mines in the area surrounding the proposed new mine and planning the layout of the new mine so that there is a safe distance between the new mine and any pre-existing mine.
A major problem with this scheme is that the maps of existing mines are frequently inaccurate or incomplete. Given this situation, even with the best possible planning the excavator of a new mine is frequently unable to completely ensure that the new mine will not intersect with a pre-existing mine. As a result, the excavator of a new mine in effect gambles that the maps of existing mines are accurate. In such situations, the inaccuracy of old maps is usually not realized until disaster has already struck.
In addition, due to the danger, expense, and regulation against human entry, it is not feasible to re-inspect abandoned mines by human means and so there is currently no way to validate maps that purport to show the layout of existing mines.
Compounding this situation is that fact that even if maps that were once accurate are available, coalfields are vulnerable to breaches, inundations and collapses. Submergence, roof fall, rotted timbers and water seals prevent human access for remapping and there is frequently no safe way to determine if such changes in the configuration of closed mines have occurred.
Given this state of affairs, it is apparent that there is a substantial and unmet need to generate accurate and complete maps of mines and other voids, even if those mines are no longer in use. One means of addressing this need is the development of robots that are capable of inspecting the internal features of a void and of obtaining data so that a precise map of existing conditions could be generated. Use of a robot for this work has several advantages over competing technologies. For example, the physical presence by a robot inside underground cavities is proof of the existence of void at that location. The direct observation of the surface of an internal cavity is superior to complementary approaches (e.g., ground penetrating radar or seismic technique) that only make inference from external observation.
Use of robotics for mapping mines offers the possibility of generating survey quality mapping of those mines, as opposed to the results of competing technologies which only provide approximations of the location of voids which may or may not be mines. Not only would a two-dimensional (2D) layout of the mine be obtainable from the use of such robots, but such robotics could model three-dimensional (3D) surfaces such as the roof, walls and floors of such a mine. In addition, small robots would be capable of accessing confined voids that might be completely undetectable by complementary approaches.
Some work in the development of mine mapping robots was performed at Carnegie Mellon University in the early 1990's. For example, early attempts at mine mapping (circa 1993) included a robot developed by some of the present inventors which mapped and navigated a portion of a coal mine. In this experiment, local navigation software and acoustic sensing was integrated with a composite model builder. The robot traversed a short piece of the mine mapping the walls and creating a network of goal positions.
Subsequent experiments with the same robot included using data from a scanning laser range finder and making turning decisions based on its internally generated map. This early robot had both an under-powered onboard computer and such a large power consumption as to be unfeasible for practical work. It also was not capable of working in water- or explosive gas-filled environments.
Other researchers have also investigated the use of robots in mines and wells. For example, U.S. Pat. No. 4,884,847 discloses a vehicle equipped with numerous types of sensors to create maps of mines. The vehicle is guided remotely, and a data link such as a fiber optic cable is used to transmit data back to a computer located outside the mine. However, that robot can not be used to generate a map of a mine by itself; in fact, the disclosure specifically states (at col. 3, line 5) that “accurate entry maps and profiles will probably not be developed by simple deduction from the instrument data; rather, a more complex, knowledge-based algorithm will be required.” In other words, some further interpretation of the data, presumably by a human, will be needed to actually generate a map of the mine.
U.S. Pat. No. 6,405,798, and U.S. Pat. No. 6,446,718 (a continuation thereof), both pertain to an autonomous vehicle which can be used to inspect conditions within an oil well, perhaps utilizing high frequency sonar and a video camera. Nothing in this disclosure refers to mapping the internal features of the well (void).
Finally, U.S. Pat. No. 6,009,359 addresses the need for a robot to map an unknown indoor environment such as an underground mine tunnel. The disclosed invention is limited to the use of a plurality of sensors that are located a known distance from one another. From the overlap and intensity of the images, the robot can calculate the distance between itself and the walls of the enclosed environment. The technology disclosed in this patent is limited to the process of generating maps from stereoscopic images. In addition, the patent does not give any indication of how to make the invention work in a possibly turbid environment which may be partially or completely filled with a liquid such as water and in which diffraction or attenuation of light would significantly degrade mapping performance. Further, the robot described in that patent requires that access to the void be at least as large as the size of the robot; no provision is made for the robot entering the mine through a small borehole and subsequently expanding into a larger, more useful configuration.
As such, there is a need in the art to provide a self-contained, autonomous robot capable of generating a map on its own or to plot a course through and around a void without direct human supervision. The present invention, in at least one preferred embodiment, addresses one or more of the above-described and other limitations to prior art systems.